Amido-carboxylic acids are industrial chemical intermediates for the preparation of many chemicals used in commerce. Amido-carboxylic acids are prepared by reacting a lactam with a carboxylic acid.
Amido-carboxylic acids are also prepared by reacting a carboxylic acid, carboxylic acid chloride, carboxylic acid anhydride or carboxylic acid ester with an amino carboxylic acid which is prepared by hydrolysis of a lactam. These processes to form amido-carboxylic acids are referred to as amidation reactions.
It is known to convert lactams by hydrolysis into the corresponding amino-carboxylic acids in the presence of hydrolysis promoting reagents such as hydrochloric acid. However, pure amino-acids are not directly obtained. In the case where hydrochloric acid is used as the promoting reagent, the amino-acid-hydrochloride is obtained and the separation of the free carboxylic acid is cumbersome and expensive.
U.S. Pat. No. 2,453,234 discloses a process for preparing an amino-carboxylic acid by hydrolyzing a lactam by means of at least 10 moles of water per mole of lactam to produce an amino-carboxylic acid. Great Britain Pat. No. 648,889 discloses a process for preparing amino-carboxylic acids by heating aliphatic or cyclo-aliphatic lactams in the presence of more than 20 moles of water per mole of lactam. U.S. Pat. No. 2,956,068 discloses a process for preparing amido-carboxylic acids by reacting a lactam with a free carboxylic acid in the presence of catalytic amounts of water. The reaction product is obtained as a solid crystal mass which is subsequently suspended in water and neutralized.
In contrast, the present inventors have unexpectedly discovered a process for preparing amido-carboxylic acids wherein lactam hydrolysis, carboxylic acid ester hydrolysis, and amidation reactions are conducted simultaneously. It is unexpected that an amido-carboxylic acid could form by amidation under hydrolysis conditions. The amido-carboxylic acids obtained by this process essentially contain one molecule of amino acid and one molecule of carboxylic acid.